Leak Size Research Articles

Escape dynamics through a continuously growing leak.

We formulate a model that describes the escape dynamics in a leaky chaotic system in which the size of the leak depends on the number of the in-falling particles. The basic motivation of this work is the astrophysical process, which describes the planetary accretion. In order to study the dynamics generally, the standard map is investigated in two cases when the dynamics is fully hyperbolic and in the presence of Kolmogorov-Arnold-Moser islands. In addition to the numerical calculations, an analytic solution to the temporal behavior of the model is also derived. We show that in the early phase of the leak expansion, as long as there are enough particles in the system, the number of survivors deviates from the well-known exponential decay. Furthermore, the analytic solution returns the classical result in the limiting case when the number of particles does not affect the leak size.

Leak Detection in a Branched System by Inverse Transient Analysis with the Admittance Matrix Method

The diagnosis of water distribution systems by means of the inverse transient analysis requires efficient and reliable numerical models. In the network admittance matrix method (NAMM) the 1-D waterhammer governing equations are integrated in the frequency domain and organized in a laplacian matrix form. The NAMM is particularly suitable for complex systems because of this structure and can be used for the system diagnosis, including leak sizing and location. In this paper a damaged branched system is considered and the diagnosis is performed by means of the NAMM using experimental data from laboratory transient tests. Two different boundary conditions are used in the implementation of the NAMM and the leak is located and sized with a reasonable approximation. An extended numerical investigation is also presented and allows confirmation of the results for different leak locations. The use of the NAMM for the leak detection and the validation using experimental data on a branched system are the main original contributions of this work. The successful diagnosis indicates promising results for applications in more complex systems.

Leak localization in water distribution networks using Bayesian classifiers

This paper presents a method for leak localization in water distribution networks (WDNs) based on Bayesian classifiers. Probability density functions for pressure residuals are calibrated off-line for all the possible leak scenarios by using a hydraulic simulator, and considering the leak size uncertainty, demand uncertainty and sensor noise. A Bayesian classifier is applied on-line to the computed residuals to determine the location of leaks in the WDN. A time horizon based reasoning combined with the Bayesian classifier is also proposed to improve the localization accuracy. Two case studies based on the Hanoi and the Nova Icària networks are used to illustrate the performance of the proposed approach. Simulation results are presented for the Hanoi case study, whereas results for a real leak scenario are shown for the Nova Icària case study.

Zinc treatment is efficient against Escherichia coli \u03b1-haemolysin-induced intestinal leakage in mice

Zinc homoeostasis exerts protective effects in inflammatory intestinal diseases and zinc supplementation has been successfully used for treating infectious diarrhoea. This study aimed at a characterisation of zinc effects on focal leak induction by α-haemolysin (HlyA)-producing Escherichia coli (E. coli) as protective mechanism for colitis. We conducted in vivo experiments by oral challenge of gnotobiotic mice colonised with HlyA-expressing E. coli-536. Mice were either fed a defined normal or high zinc diet to analyse effects of zinc as a therapeutic regimen. HlyA-deficient E. coli-536 mutants were used as controls. Mice infected with HlyA-producing E. coli showed impaired barrier integrity when receiving normal zinc. High zinc supplementation in HlyA-producing E. coli-infected mice reduced epithelial dysfunction as indicated by ameliorated macromolecule permeability. Reduced size of focal leaks with diminished bacterial translocation was observed as inherent mechanisms of this zinc action. In human colon cell monolayers application of zinc rescued the HlyA-dependent decline in transepithelial electrical resistance via reduction of the calcium entry into HlyA-exposed cells. Calcium-dependent cell exfoliation was identified as mechanism for focal leak induction. In conclusion, zinc supplementation protects from HlyA-induced barrier dysfunction in vivo and in vitro, providing an explanation for the protective efficacy of zinc in intestinal disorders.

Theoretical and experimental investigation of magnetic field related helium leak in helium vessel of a large superconducting magnet

The helium vessel of the superconducting cyclotron (SCC) at the Variable Energy Cyclotron centre (VECC), Kolkata shows a gradual loss of insulation vacuum from 10−7mbar to 10−4mbar with increasing coil current in the magnet. The insulation vacuum restores back to its initial value with the withdrawal of current. The origin of such behavior has been thought to be related to the electromagnetic stress in the magnet. The electromagnetic stress distribution in the median plane of the helium vessel was studied to figure out the possible location of the helium leak. The stress field from the possible location was transferred to a simplified 2D model with different leak geometries to study the changes in conductance with coil current. The leak rate calculated from the changes in the leak geometry was compared with the leak rate calculated from the experimental insulation vacuum degradation behavior to estimate the initial leak shape and size.

Outcomes and predictors of success and complications for paravalvular leak closure: an analysis of the SpanisH real-wOrld paravalvular LEaks closure (HOLE) registry.

The aim of the study was to assess the safety and efficacy of percutaneous closure of paravalvular prosthetic leak (PVL) and to identify the predictors of procedural success and early complications. A total of 514 first-attempt percutaneous PVL closure in 469 patients were included at 19 centres. Technical and procedural success was achieved in 86.6% and 73.2% of the patients, respectively. In multivariate analysis, the independent predictors for procedural success in mitral lesions were the type of device used (AMPLATZER AVP III vs. others, HR 2.68 [1.29-5.54], p=0.008) and the number of procedures performed at the centre (top quartile vs. others, HR 1.93 [1.051-3.53], p=0.03). For aortic leaks the only predictor of procedural success was the leak size (≥10 mm vs. <10 mm, HR 3.077 [1.13-8.33], p=0.027). The overall major adverse events rate (death or emergency surgery or stroke) at 30 days was 5.6%; the only predictor for combined adverse events was New York Heart Association functional Class IV (HR 4.2 [1.42-12.34], p=0.009). Percutaneous closure of PVL can be performed with a reasonable rate of procedural success and a low rate of major complications. The type of device used, the accumulated experience and the leak size are predictors of procedural success.

PUB148 Efficacy of Heimlich Valve in Preventing Air Leaks

One of the most common complications after a lung reduction surgery is prolonged air leak. This is a prospective study, which reports the routine use of Hiemlich valve and its impact on total hospital stay and a reoperation for a persistent leak. This article evaluates a type of treatment for air leaks using Hiemlich valves; the results also show a prospective algorithm for treatment of persistent air leaks. From September 2005, through November 2011, 150 patients were operated for elective pulmonary resection, which had a heterogenous pattern of lung disease, with post-operative mortality of 4 patients and average duration of total length of hospital stay of 10.61 days. Bilateral Hiemlich valves were applied to 18 patients, and unilateral Hiemlich valves in 132 patients. Dyspnea increased in 10 patients after switching to Heimlich valve and they were resumped on chest drainage with suction.Use of Heimlich valve was done irrespective of size of air leak. Grading of air leak was done as small defined if an occasional bubble was seen; moderate when frequent bubbles were seen or large if the bubbles were continuous in the water seal chamber. X-rays were obtained in patients after Hiemlich valve was placed which showed minimal size of air leak. Patients did not develop dyspnea after placement of Hiemlich valve. Follow up x-rays in all of the cases after removal of Hiemlich valve showed completely resolved apical air spaces. Mean number of postoperative days to placement of the Hiemlich valve was 7.2 ± 2.4. The mean number of days to postoperative discharge was 8.1 ± 1.6(range5 to 16) and the mean number of days after discharge until removal of the chest tubes and the Hiemlich valves was 3.61 ± 1.4(range 0, to 26). Almost all patient tolerated Hiemlich valve well after discharge. The average hospital stay was shortened by 56% with the use of Hiemlich valve in patients who underwent lung reduction surgery, considering the fact that all these patients would have stayed in the hospital, till the removal of their chest tube. The mean length of hospital stay was 11 days. The reduced hospital stay has certainly been caused by the use of Hiemlich valve. It is advisable to put chest drainage system to Hiemlich valves, as early as the third post-operative day. This eventually helps in providing better patient care.

Pressure buildup test analysis in wells with sustained casing pressure

When the well's casing head pressure cannot be permanently bled off with a needle valve, the casing is said to exhibit Sustained Casing Pressure (SCP). Rebuilding of surface pressure (pressure buildup – after closing the valve) results from migration of gas in the leaking cement sheath of the well's annulus. Problem of sustained casing pressure (SCP) has been widespread in the Gulf of Mexico and also reported in Canada, Norway, and other places. Regulations require 24-hr testing of SCP wells comprising pressure bleed-down followed with pressure buildup. In these tests, the rate of pressure buildup is indicative of the size of cement leak – prompt buildup implies larger leak on a relative scale with no quantification. Presented here is the first mathematical model for quantitative analysis of pressure buildup in SCP wells. The model simplifies transient gas flow in cement and ignores migration time of gas in the annular fluid column above the cement top. The simplification allows finding the size of cement leak and the depth and value of gas pressure source formation.Also presented is validation of the model with actual field data from testing SCP wells. Matching the model to field data gives acceptable estimates of the gas-source formation depth and pressure, cement leak size, and expected maximum casing pressure value. The results also reveal a correlation between the pressure buildup-stabilization pattern and well parameters - cement leak size controls the pressure buildup rate, while the gas-source formation pressure controls the stabilized pressure value. Quantitative analysis of SCP buildup with the new model could be extremely useful as it provides values of three parameters (cement leak size, gas source formation depth and pressure) that are critically important for designing remedial treatment.

Determination of design accidental fire load for offshore installations based on quantitative risk assessment with treatment of parametric uncertainty

This study investigated the critical issues for determining the design accidental load (DAL) fire procedure based on quantitative risk assessment (QRA) for offshore installations. Considerable attention was paid to parametric uncertainty in choosing the numerical values used for the frequency and consequence analysis. In particular, selecting the initial leak size was one of the most critical aspects, and inconsistent approaches for selecting this value resulted in different risks for identical systems. Frequency analysis of past investigations also overlooked the inaccuracy and unsuitability of statistical data. Accordingly, the estimated risks were significantly uncertain, and the lack of information about the results increased the risk of making the wrong decision. In this study, the Latin hypercube sampling (LHS) technique was used to treat parametric uncertainty in QRA. Different fire exceedance curves and DAL fires were demonstrated by selecting different sets of representative values. The distribution and confidence interval of the DAL fires showed a wide distribution with varying uncertain and critical parameters. Therefore, this procedure provided quantitative information on inherent uncertainty, and such additional information regarding DAL fires can lead to better decision making.

Optimal control of fuel overpressure in a polymer electrolyte membrane fuel cell with hydrogen transfer leak during load change

Formation of membrane pinholes is a common defect in fuel cells, inflicting more cost and making less durable cells. This work focuses on mitigating this issue, and offers a continuous online treatment instead of attempting to dynamically model the hydrogen transfer leak rate. This is achieved by controlling the differential pressure between the anode and cathode compartments at the inlet side of the fuel cell stack, known as the fuel overpressure. The model predictive control approach is used to attain the objectives in a Ballard 9-cell Mk1100 polymer electrolyte membrane fuel cell (PEMFC) with inclusion of hydrogen transfer leak. Furthermore, the pneumatic modeling technique is used to model the entire anode side of a fuel cell station. The hydrogen transfer leak is embedded in the model in a novel way, and is considered as a disturbance during the controller design. Experimental results for different sizes of hydrogen transfer leaks are provided to show the benefits of fuel overpressure control system in alleviating the effects of membrane pinholes, which in turn increases membrane longevity, and reduces hydrogen emissions in the eventual presence of transfer leaks. Moreover, the model predictive controller provides an optimal control input while satisfying the problem constraints.

Effect of full-bore natural gas release on fire and individual risks: A case study for an LNG-Fueled ship

This study investigated the significance of categorizing and selecting representative leak sizes in Quantitative Risk Assessment (QRA) for estimating natural gas fire risks. In most fire QRA procedures, the full-bore sizes of leaks have been overlooked even though they causes the catastrophic consequences with relatively high frequencies. So, in the present study, the effect of particular leak sizes on the individual risks (IRs) were investigated through the fire risk assessment. As case studies, LNG (Liquefied Natural Gas) fuel gas supply system for a large ship were considered with three different approaches. Approach 1 considers only three categories of leak sizes; small, medium, and large. Approach 2 includes the full-bore leak in addition to categories of Approach 1, and Approach 3 reflects more categories of leak sizes with every 1 mm increment in diameter. Compared with the total IR of Approach 3, the total IR of Approach 1 was two times lower, whereas Approach 2 resulted in the comparable total IR with an approximately 4% deviation. Admitting that Approach 3 should be close to the exact solution, Approach 2 gave acceptable results, whereas Approach 1 unsatisfactorily underestimated the total IR. The results indicated that full-bore leak accidents are critically important scenarios and omission of them can lead to misjudgment in the risk-informed decision-making process. Taking the full-bore accidents into additional account to the conventional simplified QRA can reduce the time and effort for estimating the leak-related risks without a significant loss of accuracy in the estimated risks.

Numerical studies on the performance of an aerosol respirator with faceseal leakage

We studied the efficiency of a facepiece filtering respirator (FFR) in presence of a measurable faceseal leakage using the previously developed model of a spherical sampler with porous layer. In our earlier study, the model was validated for a specific filter permeability value. In this follow-up study, we investigated the effect of permeability on the overall respirator performance accounting for the faceseal leakage. The Total Inward Leakage (TIL) was calculated as a function of the leakage-to-filter surface ratio and the particle diameter. A good correlation was found between the theoretical and experimental TIL values. The TIL value was shown to increase and the effect of particle size on TIL to decrease as the leakage-to- filter surface ratio grows. The model confirmed that within the most penetrating particle size range (∼50 nm) and at relatively low leakage-to-filter surface ratios, an FFR performs better (TIL is lower) when the filter has a lower permeability which should be anticipated as long as the flow through the filter represents the dominant particle penetration pathway. An increase in leak size causes the TIL to rise; furthermore, under certain leakage-to-filter surface ratios, TIL for ultrafine particles becomes essentially independent on the filter properties due to a greater contribution of the aerosol flow through the faceseal leakage. In contrast to the ultrafine fraction, the larger particles (e.g., 800 nm) entering a typical high- or medium-quality respirator filter are almost fully collected by the filter medium regardless of its permeability; at the same time, the fraction penetrated through the leakage appears to be permeability- dependent: higher permeability generally results in a lower pressure drop through the filter which increases the air flow through the filter at the expense of the leakage flow. The latter reduces the leakage effect thus improving the overall respiratory protection level. The findings of this study provide valuable information for developing new respirators with a predictable actual workplace protection factor.

Role of lumbar drains in contemporary endonasal skull base surgery: Meta-analysis and systematic review.

Historically, lumbar drains (LD) have played a prominent role in endonasal skull base surgery. Over the past few decades, advancements in techniques have augmented our ability to successfully reconstruct complex skull base defects and often obviates the need for cerebrospinal fluid (CSF) diversion. Clarity on the appropriate use of LDs is needed. To examine the literature for the need for LDs in contemporary skull base reconstruction after resection of skull base tumors. A systematic literature review of English language articles by using PubMed and Ovid. Search terms included "lumbar drain," "CSF leak," and "endoscopic endonasal reconstruction." Articles were included when they pertained to adults, used current methods for reconstruction (i.e., multilayered repair or vascularized tissue), and addressed CSF leak rates secondary to endoscopic resection of skull base masses. All the studies discussed CSF leaks that resulted from traumatic-, idiopathic-, or sinus surgery-related iatrogenic causes were excluded. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed. A total of five articles met inclusion criteria. These comprised 376 endoscopic skull base tumor resection and reconstruction cases; 5.59% developed postoperative CSF leaks. A meta-analysis was conducted by incorporating three studies that met criteria based on testing for heterogeneity. The average odds ratio for postoperative CSF leak for patients who did not have an LD relative to patients who had an LD was 0.590 (95% confidence interval, 0.214-1.630). Given a p value of 0.30, the results demonstrated a lack of statistically significant improvement between patients who had an LD and patients who did not have an LD. Various details, such as the defect size and type of CSF leak, were not consistently reported among studies. Available evidence for the use of LDs in skull base surgery is of poor quality. Analysis of the literature revealed heterogenous and varied reporting in the primary literature. Further studies that include randomized controlled trials are needed.

Methane Leaks from Natural Gas Systems Follow Extreme Distributions.

Future energy systems may rely on natural gas as a low-cost fuel to support variable renewable power. However, leaking natural gas causes climate damage because methane (CH4) has a high global warming potential. In this study, we use extreme-value theory to explore the distribution of natural gas leak sizes. By analyzing ∼15 000 measurements from 18 prior studies, we show that all available natural gas leakage data sets are statistically heavy-tailed, and that gas leaks are more extremely distributed than other natural and social phenomena. A unifying result is that the largest 5% of leaks typically contribute over 50% of the total leakage volume. While prior studies used log-normal model distributions, we show that log-normal functions poorly represent tail behavior. Our results suggest that published uncertainty ranges of CH4 emissions are too narrow, and that larger sample sizes are required in future studies to achieve targeted confidence intervals. Additionally, we find that cross-study aggregation of data sets to increase sample size is not recommended due to apparent deviation between sampled populations. Understanding the nature of leak distributions can improve emission estimates, better illustrate their uncertainty, allow prioritization of source categories, and improve sampling design. Also, these data can be used for more effective design of leak detection technologies.

Use of above-zone pressure data to locate and quantify leaks during carbon storage operations

We determine the potential accuracy in estimating the size and location of leaks in the caprock by history-matching above-zone pressure monitoring data to leakage models. The number of monitoring wells and the total monitoring time is varied in order to determine minimum pressure-monitoring requirements for effective leak characterization. The history-matching procedure uses particle swarm optimization to minimize the error between leakage-model solutions and synthetic observation data by adjusting model parameters governing the size and location of the leak, as well as the heterogeneous permeability field throughout the model. The method applies to storage projects with uncertain heterogeneous geology that may be described by a variogram model. Results from several examples indicate that as little as 6–12 months of above-zone pressure monitoring data, collected from at least 3 or 4 wells, may be sufficient to locate and estimate the size of a leak to inform mitigation and remediation strategies. No significant benefit is seen when using multilevel monitoring wells versus single-level monitoring wells. We also find that adding white noise to the synthetic observation data, with magnitude consistent with current pressure monitoring techniques, generally reduces error in solutions, likely due to a regularization effect. Taken in total, the results and procedures introduced in this study should be of use in designing monitoring strategies in large-scale carbon storage projects.

Parametric generation of explosion scenarios for quantitative risk assessment of gas explosion in offshore plants

In this study, probabilistic risk assessment has been carried out for the prediction of gas explosion loads due to hydrocarbon leaks and subsequent explosions in the topside of offshore platforms. In the initial phase of the risk assessment, the effect of various scenario parameters on the annual probability of gas explosion was quantified via a MATLAB code. For calculating the gas explosion frequency, the hydrocarbon leak frequencies and the ignition probabilities were derived from the HCR (HydroCarbon Release) database from the Health &amp; Safety Executive (HSE, UK), and the IP (Ignition Probability) report from UKOOA (UK Offshore Operators Association), respectively. The MATLAB code has the algorithm to cope with the varying design practice in either Front End Engineering Design phase or detailed design phase. User‐definable parameter setup and spreadsheet data input provide the user with the flexibility in selecting relevant level of elaboration for such design parameters as the leak size distribution, the hydrocarbon composition, etc. These features of the code enable controlling the number of explosion scenarios without any parameter range remaining unaccounted for. The present MATLAB code has been applied to generate hydrocarbon leak scenarios and corresponding explosion probability for the topside process modules of a specific oil Floating Production, Storage and Offloading. Varying the number of cases for each parameter leads to the variation of the number of explosion scenarios selected, which are either 48 or 24 in the particular case. For each explosion scenario, the gas leak and explosion simulation was carried out using the FLame Acceleration Simulator (FLACS) commercial S/W package, giving rise to the annual probability of exceedance for the explosion overpressure. Discussion of the influence of explosion scenario selection method on the change of the overpressure exceedance curves is made. © 2016 American Institute of Chemical Engineers Process Saf Prog 36: 139–149, 2017

Inducing arbitrary vapor pressures, and quantifying leakages

We generalize the Maxwell drop evaporation equation to cover the range from closed system to open system through semiclosed system where the evaporation is restricted to an arbitrary degree which we show how to characterize. We first consider a suspended drop, and then a drop contacting a surface where the surface's vicinity restricts the evaporation paths. We show how to use these results to obtain arbitrary values of vapor pressure by simple manipulations of the numbers and sizes of droplets added to the system for a constant leak size, or, alternatively, control the leak size with a valve for given sizes of drops. We further show how to use this result to quantify a leakage in a system. Such a leakage is characterized using a single parameter (leakage length) which the described method calibrates. The calibrated leakage length can be used for systematic control of vapor concentrations within the chamber. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4548–4553, 2016

Electro-magnetic stress-induced degradation of insulation vacuum of a large cryo-magnetic system

In superconducting magnets, the cold mass is placed in a vacuum vessel to reduce heat load to the liquid helium system. Helium leaks into the vacuum vessel can degrade the insulation vacuum, which can, in turn, cause an increase in the heat load to the liquid helium system. These leaks are called cold leaks, as they show up when the coil is cooled with liquid helium. K500 superconducting cyclotron magnet at Variable Energy Cyclotron Centre, Kolkata has such cold leaks in the helium vessel that developed during cool down. The leak rate increases with the increase of current in the superconducting coils. This paper describes a series of experiments carried out on the superconducting cyclotron magnet to find the level of degradation of insulation vacuum and measure the increase in heat load with magnet current. The leak rate was also measured and the leak size was estimated analytically. Detail magneto-structural analysis was done using Finite Element Method (FEM) to identify highly stressed zones in the helium vessel and found out that highly stressed zones coincide with the weld zones. The magneto-structural stress was applied on an estimated size of single crack and found that crack tip stress could reach beyond elastic limit of the material. We can predict that the full design current may be unachievable in this situation. Mitigation of increased heat load was also done using an additional vacuum pump for the insulation vacuum space.

Experimental Evaluation of LPG Release and Dispersion in the Enclosed Car Parks

Despite the fact that LPG is used in a large number of cars, tests have not yet been carried out on whether parked cars in enclosed garages are a greater threat than petrol cars. The problem of LPG-powered vehicles in enclosed car parks applies to both public and industrial areas.This paper describes real scale tests, which demonstrate conditions that can occur in a garage in the event of LPG release from a car installation. The validation of FDS code (NIST) for using in the case of modelling LPG release and dispersion in different situations is also described. Over the course of the tests, a series of six real scale LPG spillage experiments were performed to study emission time and cloud formation according to the leak size in the car installation. As a tested scenario, the release of 0.17 L of LPG in liquid phase, from the pipe connecting the tank and the engine, was used. On the basis of these measurements results, the distribution of LPG in the garage was obtained. The test results were used to create the optimal CFD model of LPG outflow and validation of FDS code against simulations of LPG gas release and dispersion.

Artificial Leaks in Container Closure Integrity Testing: Nonlinear Finite Element Simulation of Aperture Size Originated by a Copper Wire Sandwiched between the Stopper and the Glass Vial.

Container closure integrity (CCI) testing is required by different regulatory authorities in order to provide assurance of tightness of the container closure system against contamination, for example, by microorganisms. Microbial ingress CCI testing is performed by incubation of the container closure system with microorganisms under specified testing conditions. Physical CCI uses surrogate endpoints, such as coloration by dye solution ingress or gas flow. In order to correlate microbial ingress CCI and physical CCI test methods and to evaluate the methods' capability to detect a given leak, artificially created defects (artificial leaks) are being introduced into the container closure system in a variety of different ways. In our study, artificial leaks were generated using inserted copper wires between the glass vial opening and rubber stopper. Up to date, the insertion of copper wires introduced leaks of unknown size and shape. With nonlinear finite element simulations, the effective aperture size between the rubber stopper and the glass vial was calculated, depending on wire diameter and capping force, and the leak shape was modelled. Our results suggest that the size as well as the shape of the artificial leaks should be taken into account when evaluating critical leak sizes, as flow rate does not, independently, correlate to the hole size.